Vinyl Acetate Synthesis on Au/Pd(111)

CALAZA, FLORENCIA C.; LI, ZHENJUN; TYSOE, WILFRED T.

Cuernavaca

Conferencia; The Fourth San Luis Summer School and Conference on Surfaces, Interfaces and Catalysis; 2007

A Pan-American Advanced Studies Institute

Acetic acid, ethylene and oxygen react in the presence of Pd catalysts to give Vinyl Acetate, but combustion of reactants and products to carbon dioxide and water is a secondary reaction which lowers the selectivity. In the last years, the addition of gold has shown an increment in selectivity. Despite of its importance very little is known about the reaction mechanism and the role of gold for the high selectivity obtained. After having elucidated the mechanism on Pd(111), now we focus our research to the interaction of each reactant with Au/Pd(111) alloys to understand the role of gold in the reaction. The adsorption and decomposition pathways of vinyl acetate on these alloys was also studied by means of RAIRS and TPD experiments were it was found that no decomposition occurred for gold coverages greater than 0.73 and there is a strong electronic modification of palladium sites by gold as shown in the difference of desorption activation energies at low gold coverages (left figure). Some preliminary results were obtained for the synthesis of VAM over low gold composition alloys (right figure), showing important electronic effects due to Au on the surface, which in turn affect the selectivity of the reaction.